While the Covid-19 virus continues to circulate and claim victims around the world, its origin remains unknown. Each scientific community advances its hypothesis. Some suggest the possibility of an escape of the virus from a laboratory. Response elements.
What is the origin of the Covid-19 pandemic? While the SARS-CoV-2 coronavirus virus continues to circulate and claim lives around the world, its origin remains unknown. Each scientific community advances its hypothesis. Some suggest the possibility of an escape of the virus from a laboratory.
Another hypothesis, which is based on recent studies related to the Chinese market of Wuhan and others carried out in Cambodia, Laos, Japan, China and Thailand, is that of an evolution from an ancestral virus present in bats, of the Horseshoe Bat family in particular, in domestic or wild animals, then the passage of the virus from these animals to humans. Indeed, during these various studies, several viruses with genetic sequences very close to SARS-CoV-2 were isolated in these bats.
A missing link
While it has now been proven that certain species of bats naturally harbor these coronaviruses, the identity of the domestic or wild animal(s) that would have acted as a relay between them and humans – missing links – remains a mystery. The Pangolin, initially suspected, now appears more as a « collateral victim » than as one of these famous missing links. Indeed, a sequence of the coronavirus genome which was detected in Pangolins was indeed related to that of SARS-CoV-2, but the rest of the genome was genetically too far from it.
On the other hand, the pangolins on which viruses genetically close to SARS-CoV-2 were isolated had most of the time been confiscated from live animal markets, at the end of the commercial chain, and had therefore been in prolonged contact. with other animal species. It is very likely that they were contaminated along this pathway and not in their natural environment. Mink farms have also been suspected in China.
Finally, pangolins and horseshoe bats do not share the same habitats, which makes possible contact between the two species very unlikely, during which the virus would have passed from a bat to a pangolin. Civets and/or raccoon dogs could constitute an intermediate reservoir for SARS-CoV-1). Rodents or primates can also carry pathogens with zoonotic potential, such as Hantaviruses which can in particular cause hemorrhagic fever with severe renal syndrome or Filoviruses, including the Ebola disease virus.
The latter is transmitted to humans by wild animals, in particular fruit bats, porcupines and primates such as chimpanzees or gorillas, and then spreads in the human population mainly by direct contact with blood, secretions and other bodily fluids of infected people. The average case fatality rate is around 50%.
In 2013, the first cases of Ebola virus disease (EVD) were detected in West Africa. This emergence will cause more than 10,000 deaths mainly in Guinea, Liberia and Sierra Leone.
Bushmeat consumption: a risky practice
The risks of transmission from animals to humans, a phenomenon known as spillover, whether during hunting, animal handling or the consumption of wild meat are therefore real and potentially devastating.
It is the characterization and quantification of this risk, in Cambodia, that the ZooCov project has explored through a « One Health » approach, for almost two years and since the start of the pandemic, if so, and how, pathogens such as coronaviruses could be transmitted from wild animals, hunted and eaten, to humans.
Indeed, in Southeast Asia, the trade in wild animals and the consumption of bushmeat are a common practice. Often opportunistic, this consumption comes in certain communities to supplement a low-protein diet. It can also be regular and targeted. In Cambodia, out of 107 families interviewed during ZooCov, 77% said they had consumed bushmeat in the previous month.
Medicinal use is also widespread. In Vietnam, the analysis of confiscation reports of pangolins and derived products carried out between 2016 and 2020 by the Vietnamese authorities reports 1,342 live pangolins (6,330 kg), 759 dead pangolins or carcasses (3,305 kg), and of 43,902 kg of scales.
But this consumption also has a cultural and social aspect that is still poorly understood. For wealthy classes, and often in large cities, this consumption can be motivated by a need for social recognition, beliefs that the consumer of this meat appropriates the physical or physiological virtues of the animal consumed, or by a desire to challenge the consumption of industrial meat that is harmful to health. Wildlife farming to meet this demand, and/or fur production is also widespread.
In Cambodia, in the provinces of Stung Treng and Mondolkiri where forest protected areas still exist, more than 900 people who live on the outskirts of these forests were interviewed in an attempt to analyze the structures and functioning of commercial, illegal, meat of bush. Statistical analyzes are underway to identify the people most at risk of being in contact with such pathogens.
We already know that the people exposed are mainly young, middle-class men. Some communities are also more exposed than others. Sociological surveys have also made it possible to better understand the current context – the legal framework, the profiles of the players in this trade, their obstacles and their motivations, linked to the trade in wild animals and their consumption, and the evolution of this context. over the various health crises (Avian flu, Ebola, SARS-CoV-1, etc.).
Which populations may be at risk?
These successive crises seem to have little impact on the practices of these communities. Beyond regular consumption, a quarter of the families interviewed still reported hunting or trapping, and 11% said they sold bushmeat and/or wild animals. In addition, and in the same study sites, more than 2000 samples of wild animals subject to trafficking or subsistence consumption – bats, rodents, turtles, monkeys, birds, wild pigs, etc have been analyzed.
Some of the samples tested positive for coronaviruses in particular, and are being analyzed at the Institut Pasteur du Cambodge (IPC) to sequence the genome and learn more about its origin, evolution and zoonotic potential. Finally, blood samples were taken from more than 900 people surveyed in the same area to find out if they had been in contact with one or more coronaviruses. The analyzes are still in progress, but we already know that these people had not, at the time of the investigation, been exposed to SARS-CoV-2.
The Covid crisis has clearly demonstrated this: it is essential to detect these emergences early in order to put in place measures as quickly as possible to prevent the spread of pathogens. And if many questions remain about the mechanisms of emergence, the same logically goes for the surveillance systems to be put in place to monitor them.
The results of the ZooCov project will be used to develop a system for the early detection of spill-over events of zoonotic viruses, in particular by strengthening the wildlife health surveillance system already existing in Cambodia and set up by the Wildlife Conservation. Society WCS. Other important research and development projects will contribute to the understanding of these emergence phenomena, to their prevention and to their early detection.
The original version of this article was published in The Conversation.
